High vacuum ejector pump with automatic cut-in valve



March s, 196s A. M. WHYTE 3,239,131

HIGH VACUUM EJECTOR PUMP WITH AUTOMATIC CUT-IN VALVE Filed March 18,1963 2 Sheets-Sheet 1 l@ lll-i @gg i INVENTOR /vp/PEW M. ifi/#V75 WM dW@ A. M. wHYTE 3,239,131

HIGH VACUUM EJECTOR PUMP WITH AUTOMATIC CUT-IN VALVE March 8, 1966 2Sheets-Sheet 2 Filed March 18, 1965 INVENTOR.

AWD/25W M. M/ v7.5

United States Patent O 3,239,131 HIGH VACUUM EJECTOR PUMP WITH AUTUMATICCUT-IN VALVE Andrew M. Whyte, Norwalk, Conn., assiguor to The NashEngineering Company, South Norwalk, Conn., a corporation of ConnecticutFiled Mar. 18, 1963, Ser. No. 265,944 8 Claims. (Cl. 23o-45) Thisinvention relates to improvements in high vacuum pumping systemsutilizing a liquid ring vacuum pump in series with an atmosphere airejector pump, and in par ticular to a system which automaticallyactuates the ejector pump when the vacuum in the system has reachedpredetermined conditions.

The present invention employs a high performance evacuation system suchas represented by Patent No. 3,064,878. Such a system employs an airejector pump connected in series with a conventional liquid ring vacuumpump. In the system represented by the prior art a primary vacuum pumpproduces a vacuum of predetermined degree during the hogging operation.At this point the ejector pump is introduced into the system andactuated, thereby enabling the overall system to attain a higher degreeof vacuum than that reached by the primary vacuum pump alone.

Heretofore, in the prior art it was necessary to utilize a complicatedsystem of manually operated valves to introduce the ejector pump intothe system. In addition, the prior art required an operator to cut inthe ejector pump when the primary pump had produced a maximum vacuum. Itcan be understood that such a system, requiring the constant supervisionof an operator, added to the cost of the operation of the system.

The prevent invention simplies and improves the reliability ot priorsystems for controlling the operation of an air ejector with a liquidring pump. This is accomplished by introducing into the system anejector actuating valve with its corresponding valve elements andconduits to implement the automation and reduce the complexity of theejector pump cut in system.

In accordance with the invention, the ejector pump is retained in itsnon-operating position until the vacuum of the system has reached apredetermined degree, at which point the ejector valve is actuatedthereby providing access by the ejector pump to the atmosphere. Thus theejector pump is brought into operation automatically at a predetermineddegree of vacuum, produced by the primary pump, in the system.

It is, therefore, an object of the present invention to provide anautomatic high vacuum evacuation system.

It is another object of this invention to provide a method and means foran improved vacuum system.

It is still another object of the present invention to provide a valvefor actuating an ejector pump at a predetermined degree ot vacuum in thesystem.

It is a further object of the present invention to provide a simpler andmore reliable high vacuum evacuation system.

The present invention utilizes an ejector pump including a supersonicjet diffuser element; a uid combining chamber and a nozzle elementhaving optimum fluid ow at supersonic velocity which will be in excessof mach number unity. When the ejector pump is actuated after theprimary pump has evacuated the system to a predetermined degree ofVacuum a supersonic fluid flow is produced in the pump. The supersonicflow is sustained by the combination of a primary and secondary streamof fluid, the primary iluid being withdrawn from the container to beevacuated by the primary pump and the secondary stream withdrawn from asource such as the atmosphere, through the utilization of the vacuumproduced 3,239,131 Patented Mar. 8, 1956` by the primary pump and thecontrol valve which is an object of the present invention.

The two streams are mixed in a passage of predetermined size and shapewhere the mixed stream is decelerated, thereby increasing the pressureof the system and reducing the amount of work required to operate theprimary pump.

When ordinary air expands through a supersonic type nozzle from 14.7pounds per square inch absolute (p.s.i.a.) to pressure in the vicinityof a half-inchof mercury absolute, it attains a velocity several timesthat of sound. Neglecting friction the total pressure on the upstreamside of the nozzle is equal to that on the downstream side. The upstreamside pressure is all static and the downstream pressure is all velocitypressure. This high velocity air has the ability to entrain additionalair or other gases and vapors, and to accelerate them from stagnation orrest to a relatively high velocity. This part of the process is one ofmixing fluids during which the Velocity of the motive air and entrainedair is still supersonic after mixing, but considerably lower than thevelocity of the secondary iluid or motive air at the nozzle.

The mixture, still at supersonic velocity, enters a diffuser portionwhich greatly reduces its Velocity and increases its pressure at thedischarge end of the tube. The action taking place in the diffuserportion is the reverse of that which takes place in the nozzle. In thenozzle static pressure or head is changed to velocity head while in thedilfuser velocity head is changed to pressure head. The phenomenon canbe applied expediently to an atmospheric air operated device discharginginto the suction of a liquid ring vacuum pump.

If, for example, a supersonic jet diuser of the invention is set up todischarge into the inlet of a liquid ring pump of the kindillustratively described herein, the vacuum at the supersonic jetdiffuser suction may be 29.5 inches of mercury and simultaneously avacuum at the suction of the primary pump may be about 26 inches ofmercury. This would compare with a normal vacuum at the pump suction forthe pump alone of 28.5 inches of mercury and an eiective vacuum of thesame value. The addition of the supersonic jet dituser increases theeiective vacuum and at the same time reduces the pump suction vacuum. Atthis lower intake vacuum useful life of the pump or of the evacuationsystem and its air handling ability are both greatly increased.

While certain objects have been set forth above, other and furtherobjects will become apparent upon reading the following specificationtogether with the accompanying drawing forming a part hereof.

In the drawings:

FIG. 1 is a side elevational view, partly in section, of a high vacuumevacuation system according to the invention; and

FIG. 2 is an enlarged cross section view of the control valve of FIG.l.;

FIG. 4 is a side elevational View, partly in section of a furtherembodiment of the system shown in FIG. l;

FIG. 3 is an enlarged cross sectional view of the control valve of FIG.4 with the piston unseated;

FIG. 5 is an enlarged cross sectional view of the control valve of FIG.4 with the piston seated;

FIG. 6 is a section taken along line 6 6 of FIG. 3.

Referring now to the drawings, there is shown in FIG. l a primary vacuumpump 10 driven by motor 12 through a drive coupling 11. Vacuum pump 10may be a conventional liquid ring pump, and in the embodiment describedherein a single lobe water ring vacuum pump is employed. The pump andmotor are mounted by conventional means upon a common support 14.

A detailed description of the primary pump is not included in thisspeccation since details of such a pump o are not broadly of importancein the present case and useful application of the novel automaticcontrol principle of the invention can be made with any vacuum pumpsystem employing an ancillary ejector pumping means.

An intake manifold 16 connected to the dual inlets of primary pump andextending upward therefrom is in fiuid communication with a diffuserelement 18 through fianges 19 and fixedly secured thereto by means ofbolts 20 affixed to upper section 22 of the manifold 16. In uidcommunication with section 22 and extending outwardly therefrom is anextension 24. Extension 24 includes a check valve 26 which serves todisable by-pass conduit 28 as described more fully hereinbelow. Bypassconduit 28 is connected to extension 24 through elbow 30. T-section 32provides a suitable three way connection between conduit 28, systemconnection 34 and conduit 36. Conduit 36 in turn is suitably connectedto the input of ejector pump 38 through the utilization of flanges 37and bolts 39.

Ejector pump 3S includes a housing 40 having diffuser element 18connected thereto through flange 42. Flange 42 is integrally formed withone end of the diffuser element 18, the diffuser being held in fixedrelation to housing 40 by means of bolts 44 suitably affixed to thehousing through ange 42. Housing 40 includes a primary stream chamber 46in fluid communication with diffuser element 18 and systems connection34 through input passage 48, conduit 36 and T-section 32. Dependingdownwardly within chamber 46 is a threaded element 50. Ejector nozzle 52is threadedly engaged to element S0. A sec` ondary stream chamber 54 isformed within the element 50 directly above ejector nozzle 52.

Threaded element 50 and the ejector nozzle 52 are are positioned inaxial alignment with diffuser element 13, thereby forming acommunicating passage between the primary stream chamber 46 and thesecondary stream chamber 54. The outlet of ejector nozzle 52 is spacedapart from flared portion 56 of diffuser 18 thereby forming a terminalarea at the converging inlet mixing portion 58 of diffuser 18. Ejectornozzle52 is provided with a ared portion 55 at one end thereof whichforms a convergent portion merging into a restricted portion 57 which inturn merges with a divergent portion 59 with the larger end of divergentportion 59 being spaced from ared portion 56.

In the embodiment described herein there is no particular advantage inemploying the ejector pump 38 until a vacuum of substantially above 24inches has been ob tained through the utilization of primary pump 10during the hogging operation. Up until this point has been reached,after the primary pump has been actuated, the primary uid stream fiowsfrom the system being evacuated through system connection 34, T-section32, by-pass conduit 28, elbow 30, extension 24 and into manifold 16. Aportion of the fiuid also flows through the parallel path formed byconduit 36, chamber 46 and diffuser element 18. The stream flows frommanifold 16 through primary pump 10 and is then vented into thesurrounding atmosphere through an exhaust tube (not shown).

Threadedly engaged to housing 40 and positioned directly above secondarystream chamber 54 is a control valve 62, shown more clearly in FIG. 2.Threaded extension 63, integrally formed with and depending downwardlyfrom a housing element 66, serves to engage housing 40. Piston 64,enclosed by housing element 66, is fitted within cylindrical chamber 68to slide freely therethrough. A coiled spring 70 is suitably positionedin piston 64 at the bottom portion of piston chamber 72. The upperportion of coil spring 70 abuts ange 74 within a recessed portion 76.Bolts 78 are employed to secure ange 74 to collar 80 of control valve62. A gasket 79 is interposed between ange 74 and collar 80 to provide afiuid tight connection therebetween. Adjusting washer 65, shown in FIG.2 at the bottom of piston chamber 72,

may be of various thicknesses to thereby provide a means to adjustspring 70. Thus, if a change in the `condition of the vacuum requires adifferent compression in the spring, the washer may be changed toprovide the proper compression. Coil spring 70 thus exerts a forceagainst piston 64 which normally tends to hold the piston against valveseat 82. A resilient gasket element 84 is seated within annular recess86, said recess being defined by post' 8S and annular lip 90, said liphaving a chamfered portion' 91. The gasket 34 is held in place by asuitable washer 92 and fastener 94.

A control valve conduit 96 is suitably secured at one end to inletmanifold 16 to thereby provide a communicating passage to the upperportion of control valve 62 through orifice 98. The other end of controlvalve conduit 96 engages control valve 62 through suitable connector100. A

Piston 64 includes an annular upper edge portion 104 which, when thepiston is forced upwardly against the top portion of the chamber, seatsagainst gasket I79 thereby shutting off all leakage into the systemthrough con duit 96 and orifice 98. The annulus 105 formed by por-' tion104 and the inner surface of housing element 661 serves to provide areserve air capacity at atmospheric; pressure which is built up by aslight leakage past the piston. At the lower end of housing element 66there is integrally formed therewith a finger element 106. lilci'nent106 defines .a port 108 Iwhich is open to the ambient atmosphere,thereby allowing the atmosphere to a-pply its pressure against gasketelement 84.

In the operation of the present invention, when a'vacuum ofsubstantially 26 inches has been produced, in the chamber (not shown)connected to flange 34, by the primary pump, a secondary or ejector pumpwill be automati i cally actuated as explained herebelow. It will beunderstood that the vacuums described herein are for purposes ofillustration only and other suitable degrees of vacuum may be utilizedby the present invention.

As the vacuum is built up' in the system by primary pump 10 during thehogging operation, the same degree of vacuum will be provided on bothsides of piston 64 through control valve conduit 96 and OIHCG 95 andthrough diffuser 18, air jet element 52, secondary Sifea'? chamber 54and threaded extension 63, It will he notedf however, that the area ofthe piston ex-posed to the" vacuum lat its upper end, through orifice98, is greater than lthe area exposed to the vacuum at its lower endthrough orifice K110. The combination of the unequal size of the vacuumexposed areas of the piston and the pressure exerted by the ambientatmosphere on the lower piston portion thereof exer-ts .a force whichtends to cornpress the spring 70 and open the valve. However, this forceis resisted by coil spring 70 ywhich holds the valve closed untilsufficient force is exerted on the bottom portion of the piston toovercome the tension exerted by the spring and -lift it off valve seat82. The point at which the piston begins to move off the valve seat ispredetermined by the requirements of the particular system to `whicht-he device is applied. In the present embodiment, a vacuum of 26 incheshas been chosen. Thus the attainment of 26 inches in the system throughpump `10 causes piston 64 to move off its valve seat. At this point theentire bottom area of the piston will `become exposed to atmospheric airpressure. This will accelerate the upward movement of the piston causingit to rise rapidly to the top of its travel and seat against the topportion of the piston unit.

Check valve 26, a gravity actuated valve, is arranged. to close offby-pass conduit 28 following the unseating; of piston 64 from its closedposition. The force of` gravity urges clapper |25 to its closed positionand the slight difference in pressure between the awo sides of the checkvalve serves to hold the clapper tightly closed. It is essential to themaintenance of the highlvacuum of the pump that the check valve be heldabsolutely tight., Ihu',s,

aasalei the total primary stream of 'uid will be diverted throughconduit 36, and input passage 48 into primary stream chamber 46. It willbe noted that the by-pass is not essential to the operation of thedevice. However, if a .by-pass is not u-tilized during the hoggingoperation, such an operation will be slowed due to the relatively smallsize of the remaining fluid passage.

It can be seen that immediately following the unseating of piston 64 theatmosphere, forming a secondary stream, will flow through port 108 andorifice 110 into secondary stream chamber 54. Thus, a secondary streamis provided which then passes through air jet nozzle '52 `and intochamber 46 where the secondary stream entra-ins the gas drawn throughinput passage 48. The combined primary and secondary streams aresubsequently carried through the diluser element 18 to intake manifold16.

When the vacuum in the system falls, as will be the case when theprimary pump is shut off, coil spring 70 will again exert suicient forceto overcome the atrnospheric pressure and close the valve to therebyshut off access of the ambient atmosphere to the ejector pump. Controlvalve 62 may, of course, be adjusted to accommodate for variouspressures t0 suit the conditions under which the system is operated.

In FIG. 4 there is shown a further embodiment of the present inventionemploying a conventional positive action diaphragm-operated valve |1f1|2in lieu of the check valve 26 shown in FIG. 1.

An intake manifold 114 is connected to the dual inlets of primary pump10 and is connected at its neck portion 116 to diffuser element 18.Extension 1-18 of manifold 114 includes valve 1'12. By-pass conduit 120connects extension 118 to T-section 32. Pipe :122 is connected at oneend to valve 112 and lat its other end to automatic valve 124.

Automatic valve I124 (see FIGS. 3 ,and 5) includes a housing 126 whichencloses a piston I128 positioned in cylindrical chamber 130 in a mannerwhich allows the piston to slide freely therethrough. A coil spring 132is suitably positioned in piston 128 at the bottom of piston chamber134. Spring 132 is employed in the same manner as spring 70 (in FIGS. land 2) and described hereinabove. A channel 136 running through piston128 provides a passage to a threaded aperture 138 through groove 140when the piston is lifted off valve seat 1142 as s-hown in FIG. 3. Anannular ring v144, held in Iplace by a suitable washer 146 and fastener148 serves to provide `a proper seal when piston 128 rests on valve seat142. Piston 128 also includes an annular upper edge portion 150, whichwhen the piston is forced upwardly against the washer 79 shuts off allleakage into the system through conduit 96 and orifice 98.

Housing 126 includes a threaded extension 152. Thus there is provided ameans for threadedly engaging valve 124 to housing 40 and positioningvalve 124 directly above secondary stream chamber 54. A threaded opening154 provides access to the ambient atmosphere or may be connectedthrough a pipe 156 to fluid sources such as primary pump discharge or asmay be desired.

FIG. 4 shows the relative positions of valve 112 and the piston 128 whenthe pump system is shut down or when it is operating at only modestvacuum levels. In this condition valve 124 is closed while valve 112 isopen to present a parallel intake path to manifold 114 via the ejector38 as well as via the conduit 120. After the pump is started and whenthe vacuum reaches the point at which it becomes advantageous to utilizethe ejector pump, the vacuum in the intake manifold 114, is transmittedthrough conduit 96 to the top of the automatic valve 124 to draw piston128 to the top of its stroke. The upward movement of piston 128 is rapidbecause the pressure at 154 acts upon the entire lower area of thepiston as soon as it raises off the seat 142. The upward transfer of thepiston 128 is effective to open conduit 158 to the atmosphere therebypermitting the ejector pump to begin functioning.

Simultaneously chamber is closed olf from access t6 conduit 96, and aport 160 is opened thereby allowing the passage of atmospheric airthrough channel 136, groove 140, aperture 138 and pipe 122 to the lowerside of the diaphragm 162. Because of this large differential pressureon diaphragm 162, valve 112 transfers quickly and positively to shut offthe pump intake path through conduit 120 when the ejector is inoperation.

It will be understood from the foregoing, therefore, that a higheiciency evacuation system has been provided which includes automaticactuating means for controlling the operation of a secondary ejectorpump after a predetermined degree of vacuum has been attained by aprimary pump. Such a device substantially reduces the cost of operatingthe system and in addition increases its eiciency. Furthermore, thedevice of the present inventionV is much simpler and more reliable thanthe previous devices which have been employed in the prior art.

The spectrum of application of the device comprehended by the presentinvention includes air, gas and vapor removal, and proceses such asdrying, evaporatng, distilling, deaerating, cooking, etc., whererelatively high vacuums are required,

`While specific drawings have been presented herein it is to beunderstood that the various views are for the purpose of illustrationonly and that changes and modifications may be made in the apparatuswithout departing from the spirit of the invention.

I claim:

1. A high vacuum evacuator system comprising a primary vacuum pumphaving an inlet and an outlet, a suction conduit adapted to be placed incommunication with a device which is to be evacuated, an ejector pumpinterposed between and communicating with said suction conduit and saidinlet of said primary vacuum pump for operating in series with saidprimary vacuum pump for creating in said suction conduit a pressurelower than that which could be achieved by the primary vacuum pumpitself, valve means operatively connected to said pumps and having aclosed position cutting off communication between said ejector pump anda source of motive uid therefor, so that when said valve means is in itsclosed position said ejector pump does not operate, said valve meansautomatically responding to achievement of a predetermined degree ofvacuum by said primary vacuum pump for substantially instantaneouslymoving from said closed position to a fully open position rendering saidejector pump substantially instantaneously fully operative, so that saidejector pump will then provide in said suction conduit a lower pressurethan that achieved by said primary vacuum pump.

2. A system as in claim 1 wherein said valve means includes a pistonhaving one end surface exposed to the vacuum produced by the primaryvacuum pump and an opposite end surface having in a closed position ofsaid valve means an inner area of smaller size than said one end surfaceexposed to said vacuum and an outer area surrounding said inner area andexposed to said source of motive fluid for said ejector pump,

3. A system as in claim 2 wherein said valve means includes a springtending to keep said valve means closed until a predetermined vacuum isachieved by said primary vacuum pump.

4. A high vacuum evacuator system comprising a primary vacuum pumphaving an inlet and an outlet, a suction conduit adapted to be connectedWith a device which is to be evacuated, an ejector pump interposedbetween and communicating with said inlet of said primary vacuum pumpand said suction conduit for acting in series with said primary vacuumpump for producing in said suction conduit, and a device connectedthereto, a pressure lower than could be achieved by said primary vacuumpump itself, said ejector pump having a diffuser portion directlyconnected to said inlet of said primary vacuum pump and having upstreamof said diffuser portion an air inlet through which air from the outeratmosphere is adapted to enter into said ejector pump to act as a motiveliuid therefor, valve means having a closed position closing said airinlet and said valve means communicating with said inlet of said primaryvacuum pump for being displaced by the vacuum in said primary vacuumpump from said closed position to an open position uncovering said airinlet when said primary vacuum pump achieves a predetermined lowpressure, said valve means when initially displaced away from saidclosed position thereof being exposed to the outer atmosphere so as tobe automatically displaced substantially instantaneously to a fully openposition rendering said ejector pump fully operative in a substantiallyinstantaneous manner.

5. A system as recited in claim 4 and wherein an adjustable spring meansurges said valve means to its closed position so that the pressure atwhich said ejector pump is rendered operative is determined by saidadjustable spring means I 6. In a high vacuum evacuation system, aprimary vacuum pump to create an initial portion of the desired highvacuum, and an ejector pump to create a final portion of the desiredhigh vacuum, and valve means operatively connected to said pumps torender said ejector pump inoperative at low vacuum levels correspondingto said initial portion and of the desired high vacuum and respondingautomatically to the degree of vacuum provided by said primary vacuumpump for substantially instantaneously rendering said ejector pump fullyoperative at a high vacuum level corresponding7 to said final portion ofthe desired high vacuum.

7. A high vacuum evacuator system comprising a primary vacuuin pumphaving an inlet and an outlet, a suction conduit adapted to be placed incommunication with a device which is to be evacuated, an ejector pumpinterposed between and communicating with said suction conduit and saidinlet of said primary vacuum pump for operating in series with saidprimary vacuum pump for creating in said suction conduit a pressurelower than that which could be achieved by the primary vacuum pumpitself, a by-pass conduit communicating with said inlet of vsaid primaryvacuum pump and with said suction conduit upstream of the place wheresaid suction conduit communicates with said ejector pump, rst valvemeans operatively connected to said pumps and having a closed positioncutting off communication between said ejector pump and a source ofmotive Huid therefor, so that when said lirst valve means is in itsclosed position said ejector pump does not operate, said rst Valve meansautomatically responding to achievement of a predetermined degree ofvacuum by said primary vacuum pump for substantially instantaneouslymoving from said closed position to a fully open position rendering saidejector pump substantially instantaneously fully operative, so that saidejector pump will then provide in said suction conduit a lower pressurethan that achieved by said primary vacuum pump, and second valve meansin said by-pass conduit responding automatically to opening of saidfirst valve means for clos- ,ing said by-pass conduit, said second valvemeans opening said by-pass conduit when said lirst valve means isclosed, so that until said predetermined degree of vacuum is achieved bysaid primary vacuum pump, the fluid withdrawn from said suction conduitwill flow through said by-pass conduit to said primary vacuum pump, saidsecond valve means being a check valve.

8. A high vacuum evacuator system comprising a primary vacuurn pumphaving an inlet and an outlet, a suction conduit adapted to be placed incommunication with a device which is to be evacuated, an ejector pumpinterposed between and communicating with said suction conduit and saidinlet of said primary vacuum pump for operating in series with saidprimary vacuum pump for creating in said suction conduit a pressurelower than that which could be achieved by the primary vacuum pumpitself, a by-pass conduit communicating with said inlet of said primaryvacuum pump and with said suction conduit upstream of the place wheresaid suction conduit communicates with said ejector pump, first valvemeans operatively connected to said pumps and having a closed positioncutting olic communication between said ejector pump and a source ofmotive tluid therefor, so that when said first valve means is in itsclosed position said ejector pump does not operate, said rst valve meansautomatically responding to achievement of a predetermined degree ofvacuum by said primary vacuum pump for substantially instantaneouslymoving from said closed position to a fully open position rendering saidejector pump substantially instantaneously fully operative, so that saidejector pump will then provide in said suction conduit a lower pressurethan that achieved by said primary vacuum pump, and second valve meansin said by-pass conduit responding automatically to opening of saidtirst valve means for closing said by-pass conduit, said second valvemeans opening said by-pass conduit when said rst valve means is closed,so that until said predetermined degree of vacuum is achieved by saidprimary vacuum pump, the iiuid withdrawn from said suction conduit willflow through said by-pass conduit to said primary vacuum pump, saidsecond valve means being a diaphragm operated valve.

References Cited by the Examiner UNITED STATES PATENTS 299,267 5/1884Richter 230-45 312,644 2/1885 KuX 230-45 1,267,897 5/1918 Pagel 230-451,415,406 5/1922 Scones 230--111 2,282,889 5/1942 Schneider 230-1112,492,075 12/ 1949 Van Atta 230-45 2,754,841 7/ 1956 Eddy 137-4692,871,877 2/1959 Work 137-469 3,064,878 11/1962 Bayles et al. 230-45FOREIGN PATENTS 526,476 2/1954 Belgium.

DONLEY I, STCCKING, Primary Examiner, LAURENCE V. EFNER, Examiner.

1. A HIGH VACUUM EVACUATOR SYSTEM COMPRISING A PRIMARY VACUUM PUMPHAVING AN INLET AND AN OUTLET, A SUCTION CONDUIT ADAPTED TO BE PLACED INCOMMUNICATION WITH A DEVICE WHICH IS TO BE EVACUATED, AN EJECTOR PUMPINTERPOSED BETWEEN AND COMMUNICATING WITH SAID SUCTION CONDUIT AND SAIDINLET OF SAID PRIMARY VACUUM PUMP FOR OPERATING IN SERIES WITH SAIDPRIMARY VACUUM PUMP FOR CREATING IN SAID SUCTION CONDUIT A PRESSURELOWER THAN THAT WHICH COULD BE ACHIEVED BY THE PRIMARY VACUUM PUMPITSELF, VALVE MEANS OPERATIVELY CONNECTED TO SAID PUMPS AND HAVING ACLOSED POSITION CUTTING OFF COMMUNICATION BETWEEN SAID EJECTOR PUMP ANDA SOURCE OF MOTIVE FLUID THEREFOR, SO THAT WHEN SAID VALVE MEANS IS INITS CLOSED POSITION SAID EJECTOR PUMP DOES NOT OPERATE, SAID VALVE MEANSAUTOMATICALLY RESPONDING TO ACHIEVEMENT OF A PREDETERMINED DEGREE OFVACUUM BY SAID PRIMARY VACUUM PUMP FOR SUBSTANTIALLY INSTANTEOUSLYMOVING FROM SAID CLOSED POSITION TO A FULLY OPEN POSITION RENDERING SAIDEJECTOR PUMP SUBSTANTIALLY INSTANTANEOUSLY FULLY OPERATIVE, SO THAT SAIDEJECTOR PUMP WILL THEN PROVIDE IN SAID SUCTION CONDUIT A LOWER PRESSURETHAN THAT ACHIEVED BY SAID PRIMARY VACUUM PUMP.